1. Field of the Invention
The present invention relates to a laser machining apparatus for carrying out laser machining for a workpiece such as a semiconductor wafer.
2. Description of the Related Art
In a semiconductor device fabrication process, the surface of a semiconductor wafer of a substantially disk shape is partitioned into a plurality of regions by dividing lines called streets arrayed in a lattice shape, and devices such as ICs or LSIs are formed in the partitioned regions. Then, the semiconductor wafer is cut along the streets to divide the regions in which the devices are formed from each other to produce individual semiconductor chips.
In order to achieve miniaturization and high performances of an apparatus, a module structure in which a plurality of devices are stacked and bonding pads provided on the stacked devices are connected has been put into practical use. The module structure is configured such that a through-hole (via hole) is formed at each of the locations, in the semiconductor wafer, at which the bonding pads are provided, and a conductive material such as aluminum connecting with the bonding pads is embedded in the through-hole (via hole).
As a method of forming a through-hole (via hole) in a semiconductor wafer as described above, a perforation method for a wafer has been proposed in which a pulse laser beam is irradiated upon a substrate, which configures a semiconductor wafer, from the rear face side to efficiently form a via hole extending to a bonding pad (refer to, for example, Japanese Patent Laid-Open No. 2007-160374). According to this technique, the optical path of a laser beam can be deflected using an acousto-optical device (AOD), and a pulse laser beam is irradiated (for example, in a circular orbit) by a plural number of times upon a region in which a through-hole (via hole) is to be formed to achieve efficient machining.
Also, as a method of forming a through-hole (via hole) in a semiconductor wafer, a laser machining apparatus has been proposed which can deflect the optical axis of a laser beam in an X-axis direction and a Y-axis direction by a galvanometer scanner (refer to, for example, Japanese Patent Laid-Open No. 2008-264805).